Optical recording medium with antistatic hard coating

ABSTRACT

The present invention concerns perfluoro-based antistatic compositions comprising 0.5 to 5.0 parts by weight of an ionic perfluoro surfactant and 0.5 to 5.0 parts by weight of a nonionic perfluoro surfactant in admixture with 100 parts by weight of nonfluorinated, copolymerizable, radiation curable prepolymers as well as antistatic hard coatings prepared from these compositions. The present invention also concerns optical recording media having such antistatic hard coatings provided on at least one surface.

FIELD OF THE INVENTION

The present invention concerns perfluoro-based antistatic compositionscomprising ionic and nonionic perfluoro surfactants in admixture withnonfluorinated, copolymerizable, radiation curable prepolymers as wellas antistatic hard coatings prepared from these compositions. Thepresent invention also concerns optical recording media having suchantistatic hard coatings provided on at least one surface.

BACKGROUND OF THE INVENTION

Optical recording media typically comprise an optical recording layerprovided on a substrate. For media such as magneto optic recordingmedium and WORM (write-once-read-many) optical recording media, theoptical recording layer is generally comprised of a thin film rare earthtransition metal alloy such as gadolinium-cobalt (Gd-Co),gadolinium-iron (Gd-Fe), terbium-iron (Tb-Fe), dysprosium-iron (Dy-Fe),Gd-Tb-Fe, Tb-Dy-Fe, Tb-Fe-Co, terbium-iron-chromium (Tb-Fe-Cr),gadolinium-iron-bismuth (Gd-Fe-Bi), Gd-Co-Bi, gadolinium-iron-tin(Gd-Fe-Sn), Gd-Fe-Co, Gd-Co-Bi, and Gd-Dy-Fe. Such alloys are described,for example, in U.S. Pat. No. 4,822,675. For media such as compactdisks, the optical recording layer may be a layer of polycarbonatehaving a patterned, information-bearing surface.

Many of the materials which are suitable for the optical recording layerreact strongly with oxygen and other elements which may be present inthe environment in which optical recording media are used. Furthermore,the substrate itself may contain impurities which react with the opticalrecording layer. Thus, transparent dielectric films may be deposited onone or both sides of the optical recording layer to protect it. Suchdielectric films are described, for example, in U.S. Pat. Nos. 4,833,043and 4,917,970.

Optionally a reflective layer may be incorporated into optical recordingmedia so that incident light that passes through the optical recordinglayer a first time is reflected and passes back through the opticalrecording layer a second time. Such reflection increases the magnetooptic rotation of incident light because the so-called Faraday effect isadded to the so-called Kerr effect. Reflective layers are described, forexample, in U.S. Pat. No. 4,822,675.

The reflective layer may be incorporated into a magnetic recordingmedium such that the optical recording layer is interposed between thesubstrate and the reflective layer. For such media, transparentsubstrates are used so that incident light passes first through thesubstrate, then passes through the optical recording layer, and then isreflected by the reflective layer back through the optical recordinglayer. Such media are known as substrate incident media. When theoptional reflective layer is disposed between the substrate and theoptical recording layer, the read and write beams will not be directedthrough the substrate. Such a medium is known as an air incident medium,although generally there is at least one layer between the opticalrecording layer and the air.

For substrate incident media, the substrate is typically formed frompolycarbonate. Polycarbonate substrates have excellent rigidity,dimensional stability, transparency, and impact strength, butunfortunately have poor abrasion resistance. Consequently, polycarbonatesubstrates are susceptible to physical damage from scratches, abrading,and the like.

To protect the substrate from physical damage, a "hard coat" layer iscoated onto the substrate to form a protective barrier between thesubstrate and the air. For example, Japanese Kokai No. JP02-260145describes a hard coat layer that is coated onto the substrate of anoptical card. The hard coat layer is formed from an electron-beam orultraviolet radiation curable resin. The hard coat layer of JapaneseKokai No. JP02-260145 also includes a surface slipping agent, i.e., alubricant.

Static charge build-up attracts dust to the hard coat layer of opticalrecording media, which can prevent read and write beams from reachingthe optical recording layer during writing or reading. Thus, it isgenerally desirable to use antistatic agents to reduce this staticcharge build-up.

Antistatic compositions must satisfy stringent requirements in order tobe suitable for use in optical recording media. In addition to providingprotection against the build-up of static charge, antistaticcompositions must be transparent as well as abrasion resistant andcompositionally stable so that the compositions remain transparent forlong periods of time. If the compositions become hazy, the amount ofincident light that reaches the optical recording layer may be reduced,thus causing an increase in bit error rate, an increase in spare sector,or a loss of data. Another requirement concerns the viscosity of theantistatic composition. To obtain an antistatic coating of uniformthickness, the antistatic composition preferably must have lowviscosity, e.g., 100 centipoise or less. The use of heat curable or hotthermoplastic compositions must also be avoided, since highertemperatures, i.e., temperatures of about 100° C. or more, can damageoptical recording media and/or adversely affect media performance.

Generally, there are two approaches to using antistatic agents with thehard coat layer. One approach involves coating the antistatic agentsdirectly onto the hard coat layer. This approach, however, generallydoes not provide long-lasting antistatic protection in that suchcoatings tend to be easy to wipe away. Another approach involvespre-mixing antistatic agents with the hard coat materials before thehard coat layer is coated onto the media. With this approach, however,the conventional antistatic agents have been used at such relativelyhigh concentrations to provide acceptable antistatic protection that theresulting hard coat layers tend to become hazy over time, show poorabrasion resistance, and delaminate from the media.

Japanese Kokai No. JP57-42741 describes an antistatic compositioncomprising a nonionic fluoride surfactant and an ionic fluoridesurfactant. The antistatic composition may be coated onto a plasticsurface by dipping or spraying, or the composition may be pre-mixed inplastics prior to the molding process. According to JP57-42741, suitableplastics include heat curable and thermoplastic materials.

Japanese Kokai No. JP61-000265 describes a coating compositioncontaining a compound having perfluoroalkyl groups at both sides of aligoethyleneoxide group. The composition is used as a protective coatingfor solid surfaces, e.g., magnetic tapes or discs.

Japanese Kokai No. JP63-208561 describes perfluorosulphonamides usefulas antistatic agents for artificial resins.

Japanese Kokai No. JP62-207352 describes antistatic resin compositionscomprising 100 parts by weight of resin and 0.05 to 10 parts by weightof an anionic perfluoro compound.

U.S. Pat. No. 4,208,466 describes the preparation of ionicfluorochemical surfactants that are useful as antistatic agents andlubricants for polymeric shapes. These surfactants may be applieddirectly to a polymeric shape or compounded with a polymeric materialprior to forming.

U.S. Pat. No. 4,623,594 describes an antistatic composition obtainedfrom an electron radiation curable prepolymer and an electron radiationreactive antistatic agent soluble in the prepolymer. Suitable antistaticagents are quaternary ammonium salts such as trialkyletherammoniumsalts.

U.S Pat. No. 4,505,990 describes antistatic compositions comprising afilm-forming synthetic resin and an alkali, alkaline earth, ammonium, oramine salt of a perfluoroalkyl sulfonic acid or carboxylic acid.

SUMMARY OF THE INVENTION

It has now been discovered that combining ionic and nonionic perfluorosurfactants with nonfluorinated, copolymerizable, radiation curableprepolymers provides improved antistatic compositions that areparticularly suitable for forming hard coat layers on optical recordingmedia. Preferred antistatic compositions of the present invention arecharacterized by low viscosity, e.g., 100 centipoise or less. Having lowviscosity, the compositions can be easily spin coated onto substrates toform extremely thin, uniform coatings. Being radiation curable, thecompositions can be quickly cured using radiation after coating to formabrasion resistant, transparent, compositionally-stable antistaticcoatings that remain transparent for long periods of time.Advantageously, curing with heat or the use of hot thermoplasticmaterials is not required, thus avoiding the higher temperatures thatcan damage optical recording media. Moreover, after curing, theantistatic coatings of the present invention show excellent adhesion topolycarbonate substrates of optical recording media. As a result, thecured compositions resist delamination, or being wiped away, during thelifetime of the media.

In one aspect, the advantages of the present invention are achieved byan antistatic composition comprising 100 parts by weight ofnonfluorinated, copolymerizable, radiation curable prepolymers, from 0.5to 5.0 parts by weight of a nonionic perfluoro surfactant, and 0.5 to5.0 parts by weight of an ionic perfluoro surfactant. The antistaticcomposition forms an abrasion resistant, transparent coating when cured.

In another aspect, the present invention concerns an optical recordingmedium having an abrasion resistant, transparent antistatic coatingprovided on at least one surface of the optical recording medium. Theantistatic coating is a cured composition obtained from reactantscomprising 100 parts by weight of nonfluorinated, copolymerizable,radiation curable prepolymers, 0.5 to 5.0 parts by weight of a nonionicperfluoro surfactant, and 0.5 to 5.0 parts by weight of an ionicperfluoro surfactant.

"Transparent" means that at least 80% of incident light of a desiredwavelength or range of wavelengths is transmitted through the coating.The light transmissive characteristics of a coating may be measuredusing a device such as a UV Spectrophotometer commercially availablefrom Shimatsu, Inc.

"Abrasion resistant" means that the coating remains visually haze-freeafter 200 cycles of rubbing the coating with a nylon cloth at a weightloading of 1000 grams using a Crockmeter apparatus commerciallyavailable from Atlas Electrical Device, Inc. According to this test, anoptical recording disk is securely adhered to the platform of theCrockmeter apparatus, while making sure that the disk lies flat and thatthe edge of the disk lines up with the mark on the platform. A nyloncloth is placed on the arm head and adjusted to be smooth and flat. Thecycle number is set at 200 and the apparatus is then operated for 200cycles. After 200 cycles, the surface of the disk is checked for haze.Generally, the disk is tested twice in 2 perpendicular directions."Haze-free" means that no band of haze visually appears in the area ofthe disk where rubbing occurred. Small scratches are acceptable and mayoccur when the disk is not mounted securely and flat on the platform orwhen the nylon cloth is wrapped incorrectly on the arm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-section of a magneto optic recording mediumcomprising an antistatic coating of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a greatly enlarged schematic cross-section through aportion of an illustrative substrate incident magneto optic ("MO")recording disk 10 of the present invention. It is to be understood,however, that the antistatic compositions of the present invention arenot limited solely to use on MO media, but rather are suitable for useon a wide variety of materials. For example, in addition to being usedwith MO disks, the antistatic compositions of the present invention areparticularly suitable for use with other kinds of optical recordingmedia such as compact disks, CD-ROM, WORM (i.e., write-once-read-many)media, and the like.

Referring now to FIG. 1, an optical recording layer 12 is provided on atransparent substrate 14. A film 16 having a reflective surface 18 isdisposed to reflect incident light 40 which will have been transmittedthrough the magneto optic layer 12 a first time back through the opticalrecording layer 12 a second time. A protective sealcoat 20 is disposedover the film 16 to protect the optical recording layer 12 from theenvironment. Optionally, transparent dielectric layers 15 and 17 may bedisposed on one or both sides of the optical recording layer 12. As isknown in the art, such dielectric layers enhance the optical signal fromthe optical recording layer 12 and also protect the optical recordinglayer 12 from oxidation or corrosion due to heat, humidity, or chemicalreactions with impurities. A hard coat layer 22 of the present inventionis provided over the substrate 14 to protect the substrate 14 fromphysical damage.

The substrate 14, optical recording layer 12, film 16, protectivesealcoat 20, and the dielectric layers 15 and 17 can be of a type knownin the art. See, for example, U.S. Pat. No. 4,917,970. However, thesubstrate 14 is preferably formed from polycarbonate in that theantistatic compositions of the present invention show excellent adhesionto polycarbonate substrates. A possible rationale for this feature ofthe invention can be suggested. It is believed that the nonfluorinated,radiation curable, copolymerizable prepolymers, being generally misciblewith polycarbonate, tend to migrate into the polycarbonate when coatedonto the substrate. As a result, the prepolymers become strongly adheredto the substrate when cured as a result of forming a cross-linkednetwork with the polycarbonate.

The hard coat layer 22 is prepared from a composition comprising 100parts by weight of non-fluorinated, radiation curable, copolymerizableprepolymers. The prepolymers may be cured using any suitable form ofradiation such as electron beam radiation or ultraviolet radiation. Itis preferred, however, that the prepolymers are photocurable, i.e.,curable with ultraviolet radiation.

Examples of suitable nonfluorinated, radiation curable prepolymersinclude the ethylenically unsaturated compounds such as acrylic,methacrylic, vinyl, and allyl functional materials. Mixtures of suchethylenically unsaturated materials may also be used in the presentinvention. Preferably the nonfluorinated, radiation curable prepolymersare acrylate or methacrylate materials, or mixtures thereof. Specificcommercially available examples of nonfluorinated, radiation curable,copolymerizable monomers include Gafgard 233 sold by GAF ChemicalCorporation, TB3070m sold by Three Bond Chemical Company of America,Inc., and EX704 sold by Dainippon Ink & Chemicals, Inc., Japan. Of thesematerials, the use of EX704 is preferred.

Preferably, substantially all of the prepolymers are monomeric in form,although polymeric or oligomeric ingredients optionally may also beused. For example, acrylate-terminated polyurethanes or polyurethanesterminated with vinyl groups may be used. However, the use of suchpolymeric or oligomeric materials tends to increase the viscosity ofsolutions of the antistatic composition. If the viscosity of solutionsof the antistatic composition is too high, i.e., greater than about 200centipoise, the solution may be unsuitable for use in the spin coatingapplications discussed below.

The antistatic composition further comprises from 0.5 to 5 parts byweight, preferably 2 to 3 parts by weight of a nonionic perfluorosurfactant, and 0.5 to 5 parts by weight, preferably 2 to 3 parts byweight of an ionic perfluoro surfactant. If less than 0.5 parts byweight of either the nonionic or the ionic perfluoro surfactant is used,the antistatic composition will be unable to effectively protect againststatic charge build-up. On the other hand, using more than 5 parts byweight of either the nonionic or the ionic perfluoro surfactant provideslittle additional antistatic protection as compared to using lesseramounts of the surfactant. Additionally using more than 5 parts byweight of either surfactant may also adversely affect the abrasionresistance, transparency, and adhesion characteristics of the resultingantistatic coating. Most preferably, the weight ratio of the nonionicperfluoro surfactant to the ionic perfluoro surfactant is about 1.

Preferably, the perfluoro segment of the nonionic and/or the ionicperfluoro surfactant comprises a straight or branched carbon chain of 4to 16 carbon atoms, preferably 8 carbon atoms. Most preferably, theperfluoro segment of the nonionic surfactant and/or the ionic perfluorosurfactant is C₈ F₁₇. Practical tests have shown that nonionic and/orionic perfluoro surfactants in which the perfluoro segment is C₈ F₁₇provide better protection against static charge build-up at comparableweight loadings relative to other nonionic and/or ionic perfluorosurfactants. Most preferably, the perfluoro segment of the nonionicperfluoro surfactant is the same as the perfluoro segment of the ionicperfluoro surfactant.

Examples of nonionic perfluoro surfactants suitable in the practice ofthe present invention include

    C.sub.n F.sub.2n+1 C.sub.m H.sub.2m OH

    C.sub.n F.sub.2n+1 CH.sub.2 O(C.sub.2 H.sub.4 O).sub.m' R"

    C.sub.n F.sub.2n+1 CH.sub.2 O(C.sub.2 H.sub.4 O).sub.m' (C.sub.3 H.sub.6 O).sub.m" R"

    C.sub.n F.sub.2n+1 SO.sub.2 N(R)(C.sub.2 H.sub.4 O).sub.m' R"

    C.sub.n F.sub.2n+1 SO.sub.2 N(R)(C.sub.2 H.sub.4 O).sub.m' (C.sub.3 H.sub.6 O).sub.m" R"

    C.sub.n F.sub.2n+1 CON(R) (C.sub.2 H.sub.4 O).sub.m' R"

    C.sub.n F.sub.2n+1 CON(R) (C.sub.2 H.sub.4 O).sub.m' (C.sub.3 H.sub.6 O).sub.m' R",

wherein

n is 4 to 16, preferably 8;

m is 1-20, and preferably 8;

m' is 1-20, and preferably 14;

m" is 0-8;

R is hydrogen or lower alkyl of 1-12 C atoms such as H, CH₃, CH₃ CH₂,and the like; and

R" is hydrogen or lower alkyl of 1-12 C atoms, and preferably is H orCH₃.

Examples of ionic perfluoro surfactants suitable in the practice of thepresent invention include

    C.sub.n F.sub.2n+1 SO.sub.3 M

    C.sub.n F.sub.2n+1 C.sub.m H.sub.2m OSO.sub.3 M

    C.sub.n F.sub.2n+1 SO.sub.2 N(R)CH.sub.2 COOM ##STR1##

    C.sub.n F.sub.2n+1 SO.sub.2 N(R)C.sub.m H.sub.2m OSO.sub.3 M

    C.sub.n F.sub.2n+1 COOM

wherein

n is 4 to 16, preferably 8;

M is Na⁺, Li⁺, K⁺, H⁺, or NH₄ +, and preferably Li⁺ ;

m is 1-10, and preferably 8;

x is 1-3, preferably 1; and

R is hydrogen or lower alkyl of 1-12 C atoms such as H, CH₃, CH₃ CH₂,and the like.

Preferably, the antistatic compositions of the present invention areapplied to optical recording media, such as the magneto optic recordingdisk 10 of FIG. 1, using the spin coating technique. Spin coating allowsan extremely uniform hard coat layer having a thickness of only 0.5 to20 microns, preferably 0.8 to 10 microns, and more preferably 5 to 7microns, to be easily and quickly formed. Advantageously, such coatingsare sufficiently thin so that it is not necessary to match the opticalindex of the hard coat layer 22 with the optical index of thetransparent substrate 14.

According to the spin coating technique, an admixture is preparedcomprising the nonfluorinated, radiation curable, copolymerizableprepolymers, the nonionic perfluoro surfactant, the ionic perfluorosurfactant, and optionally a suitable solvent. The use of a solvent isnot required. However, use of a solvent is desirable when thesurfactants are not miscible with the prepolymers, i.e., the surfactantsand the prepolymers form two liquid phases when combined. Examples ofsuitable solvents include methyl alcohol, isopropyl alcohol, N-vinyl-2pyrrolidone, mixtures of these solvents, and the like. Of such solvents,a solvent mixture of 10 parts by volume isopropyl alcohol with 1 part byvolume n-butanol or isopropyl alcohol by itself is preferred.Preferably, the resulting admixture should include a sufficient amountof solvent such that the solution has a viscosity of 100 centipoise orless, and more preferably of about 5 centipoise. Generally, forisopropyl alcohol, the use of 0.7 to 1.5 grams of solvent per totalgrams of the nonionic and ionic perfluoro surfactants has been found tobe suitable in the practice of the present invention.

The admixture is preferably prepared by first combining the ionicperfluoro surfactant with the solvent, if any. Next, the nonionicperfluoro surfactant is added with stirring. The nonfluorinated,radiation curable, copolymerizable prepolymers are then slowly added andthe ingredients are agitated for a time sufficient to obtain ahomogeneous solution. Agitation times of 30 minutes have been found tobe suitable. After agitation, the admixture should be allowed to standfor at least one hour before use.

The admixture is delivered onto the substrate 14 of the magneto opticdisk 10 using a conventional spin coating apparatus. Such an apparatusgenerally includes a dispensing needle, a syringe, and a pump.Preferably, the magneto optic disk is pre-cleaned with ionized N₂ priorto spin-coating. For admixtures having a viscosity of 5 centipoise orless, a needle pressure of 5 to 20 psi delivers a suitable amount of theadmixture onto the center of a disk in about 2 seconds when the disk isspinning at 30 to 50 rpm. Preferably, an in-line filter (0.2 to 2microns) is used to remove particles from the admixture before theadmixture is allowed to pass through the dispensing needle. Afterdelivery, a high spinoff speed of 1800 to 2400 rpm for 3 to 5 secondsprovides a thin, uniform coating. Most of the solvent, if any is used,is driven off during high speed spin-off. The wet coating should then beimmediately cured with a suitable form of radiation, e.g., ultravioletradiation, at room temperature in an oven fitted with an exhaust fan.Typically, the exhaust fan is operated during curing in order to removelow boiling, volatile components from the oven.

The particular source of radiation is not critical. As one example, amedium intensity UV-arc lamp operating at a wavelength of 280 to 365 nmand an energy of 200 to 450 mj/cm² for 4 to 6 seconds would be suitablein the practice of the present invention. When the antistaticcomposition is used with a solvent, it is desirable to let the disk sitfor a few seconds in the oven with the exhaust fan on before curing toallow additional solvent to volatilize. Alternatively, such compositionscan be cured for longer times, e.g., an additional 2 to 4 seconds,relative to antistatic compositions that have not been combined with asolvent.

For admixtures with a viscosity of greater than 35 centipoise, the sameparameters as described above may be used for spin coating. However, thesolution should be preheated to 50° to 60° C. prior to coating.

Preferably, spin coating and/or curing occurs in an inert atmosphere.For example, an atmosphere comprising 90% or more nitrogen may be used.

The invention will now be further described with reference to thefollowing examples.

EXAMPLE 1

Several compositions (Samples 1-18) of the present invention wereprepared by combining a nonionic perfluorosurfactant of the formula##STR2## an ionic perfluoro surfactant of the formula

    C.sub.8 F.sub.17 SO.sub.3.sup.- Li.sup.+,

and non fluorinated, copolymerizable, radiation curable prepolymers(TB3070M, a solution of prepolymers having 30% solids commerciallyavailable from Three Bond Chemical Company of America, Inc.) in amountsaccording to Table I:

                  TABLE I                                                         ______________________________________                                        (all units are parts by weight)                                                                     Nonionic  Ionic                                         Sample  Prepolymers.sup.1                                                                           Surfactant                                                                              Surfactant.sup.2                              ______________________________________                                         1      100           2.5       2.5                                            2      100           3.8       1.3                                            3      100           2.0       3.0                                            4      100           3.0       2.0                                            5      100           0.5       0.5                                            6      100           1.0       1.0                                            7      100           1.5       1.5                                            8      100           2.5       2.5                                            9      100           0.5       4.5                                           10      100           4.5       0.5                                           11      100           1.0       4.0                                           12      100           4.0       1.0                                           13      100           1.5       0.5                                           14      100           1.5       1.0                                           15      100           0.5       1.5                                           16      100           1.0       1.5                                           17      100           0.5       2.5                                           18      100           2.5       0.5                                           ______________________________________                                         .sup.1 Although the prepolymers were obtained from a 30% solids solution,     the parts by weight in this table refers to the actual amount of              prepolymer solids that were used.                                             .sup.2 Although the ionic perfluoro surfactant was obtained from a 40%        solution, the parts by weight in this table refers to the actual amount o     ionic perfluoro surfactant that was used.                                

To prepare Samples 1-18, 40 g of the ionic perfluoro surfactant wasslowly dissolved in 60 g of isopropyl alcohol with stirring to prepare a40% solution of the ionic perfluoro surfactant. For each sample, anappropriate amount of this solution was combined with the nonionicperfluoro surfactant with stirring. After his, the 30% solid solution ofprepolymers was combined with the surfactants, and the resultingadmixture was agitated for 30 minutes. The sample was allowed to standfor 1 hour, after which the sample was coated onto a polyethyleneterephthalate film using a No. 3 Meyer Bar. The coating was then curedusing ultraviolet radiation at a wavelength of 365 nm and an energy of240 mj/cm² for 4 to 5 seconds. Curing took place in a nitrogenatmosphere at a temperature in the range from 50° C. to 60° C.

EXAMPLE 2

A sample (Sample 19) of the present invention was prepared in accordancewith Example 1, except that CF₃ SO₃ ⁻ Li⁺ was used in place of C₈ F₁₇SO₃ ^(-Li) ⁻ as follows:

    ______________________________________                                                              Nonionic  Ionic                                         Sample  Prepolymers   Surfactant                                                                              Surfactant                                    ______________________________________                                        19      100           2.5       2.5                                           ______________________________________                                    

EXAMPLE 3

A sample (Sample 20) of the present invention was prepared in accordancewith Example 1, except that C₄ F₉ SO₃ ^(-Li) ⁺ was used in place of C₈F₁₇ SO₃ ⁻ Li⁺ as follows:

    ______________________________________                                                              Nonionic  Ionic                                         Sample  Prepolymers   Surfactant                                                                              Surfactant                                    ______________________________________                                        20      100           2.5       2.5                                           ______________________________________                                    

EXAMPLE 4

A sample (Sample 21) of the present invention was prepared in accordancewith Example 1, except that EX704, a 100% solids admixture ofnonfluorinated, copolymerizable, radiation curable prepolymers availablefrom Dainippon Ink and Chemicals, Inc. was used in place of TB3070M asfollows:

    ______________________________________                                                              Nonionic  Ionic                                         Sample  Prepolymers   Surfactant                                                                              Surfactant                                    ______________________________________                                        21      100           2.5       2.5                                           ______________________________________                                    

The viscosity of this sample was measured using a Brookfield viscometerwith a UL adaptor and determined to be 43 to 45 centipoise at 25° C. anda rotational speed of 12 rpm.

COMPARISON EXAMPLE A

5 g of the nonionic perfluoro surfactant of Example 1 was slowly addedto 300 g of TB3070 with stirring. The solution was allowed to stand for1 hour before being coated onto a PET film in accordance with Example 1.

COMPARISON EXAMPLE B

40 g of CF₃ SO₃ ⁻ Li⁺ was slowly dissolved in 60 g of isopropyl alcoholwith the help of stirring. Then, 3.8 g of this solution was added to 100g of TB3070M with stirring. The solution was allowed to stand for 1 hourbefore being coated onto a PET film in accordance with Example 1.

COMPARISON EXAMPLE C

The same procedure as Comparison Example B was followed except that C₈F₁₇ SO₃ ⁻ Li⁺ was used in place of CF₃ SO₃ ⁻ Li⁺.

COMPARISON EXAMPLE D

The same procedure as Comparison Example B was followed except that C₄F₉ SO₃ ⁻ Li⁺ was used in place of CF₃ SO₃ ⁻ Li⁺.

COMPARISON EXAMPLE E

The same procedure as Example 1 was followed except that only 0.25 partsby weight of each surfactant was used per 100 parts by weight ofprepolymer solids.

EXAMPLE 5

The antistatic properties of Samples 1-21 were compared to theantistatic properties of Comparison Examples A-E. Additionally, theantistatic properties of a PET film coated only with TB3070M (ComparisonExample F) and an uncoated PET film (Comparison Example G) were alsomeasured. Each sample was charged to about 5000 volts and the time inseconds for the charge to decay to 50 volts was measured. Thesemeasurements were made at 25° C. and 15% relative humidity. An ETS406Cmeter available from Electro Tech System, Inc. was used to monitor thecharge decay. Each sample had a size of 3.5 inches by 5.5 inches. Theresults were as follows:

                  TABLE II                                                        ______________________________________                                        Sample          Charge decay (seconds)                                        ______________________________________                                         1              0.8                                                            2              1.3 to 1.5                                                     3              0.5 to 0.76                                                    4              0.21                                                           5              1.36 to 1.58                                                   6              1.2 to 3.2                                                     7              0.7 to 0.8                                                     8              2.9 to 3.1                                                     9              0.3                                                           10              5.63 to 5.78                                                  11              0.64                                                          12              0.1                                                           13              1.2                                                           14              0.3                                                           15              0.58                                                          16              0.3                                                           17              0.36 to 0.42                                                  18              0.81                                                          19              51 to 66                                                      20              12 to 36                                                      21              2.4 to 5.0                                                    A               INFINITE*                                                     B               INFINITE                                                      C               INFINITE                                                      D               INFINITE                                                      E               INFINITE                                                      F               INFINITE                                                      G               INFINITE                                                      ______________________________________                                         *In this table, "INFINITE" means that, after 1 hour, the residual voltage     of the sample was greater than 50 volts. For all samples for which the        charge decay was INFINITE, the residual voltage of the sample after 1 hou     was at least 2000 volts.                                                 

EXAMPLE 6 a. Sample 22

An antistatic composition was prepared by slowly dissolving 40 grams ofthe ionic perfluoro surfactant of Example 1 into 60 grams of isopropylalcohol with the help of stirring. Then, 40 grams of the nonionicperfluoro surfactant of Example 1 was added into the isopropyl alcoholsolution with the help of stirring. The total weight percent of theperfluoro surfactants in the solution was around 57%. Next, 8.7 grams ofthe isopropyl alcohol solution of the perfluoro surfactants was slowlyadded into 100 grams of EX704. The solution was agitated on a shakertable for 30 minutes to mix thoroughly. After agitation, the solutionwas allowed to stand for one hour before any use.

b. Sample 23

An antistatic composition was prepared by slowly dissolving 40 grams ofthe ionic perfluoro surfactant of Example 1 into 60 grams of isopropylalcohol with the help of stirring. Next, 40 grams of the nonionicperfluoro surfactant of Example 1 was added into the isopropyl alcoholsolution with the help of stirring. The total weight percent of theperfluoro surfactants in the solution was around 57%. Next, 8.7 grams ofthe isopropyl alcohol solution of the perfluoro surfactants was slowlyadded into 300 grams of TB3070M. The solution was then agitated on ashaker-table for 30 minutes to mix thoroughly, and the mix solution wasthen allowed to stand for 1 hour before any use.

Each of Samples 22 and 23 was then spin-coated onto a magneto opticrecording disk as follows. The magneto optic recording disk wasprecleaned with an ionized N₂ gun prior to coating. The sample was thenspincoated onto the polycarbonate side of the magneto optic recordingdisk at a low air pressure (5 to 20 psi) using a needle dispensingsystem and an in-line (0.2 to 2 microns filter). The sample wasdispensed onto the center of the disk at low rpm (30 to 50 rpm) first,and a subsequent high spin-off speed (1800 to 2400 rpm) was used toachieve a smooth uniform coating. The coated disk was then cured by lowintensity UV light (365 nm) under a nitrogen atmosphere. Sample 22 had arelatively high viscosity at room temperature and was preheated to 50°C. to 60° C. prior to spincoating.

For comparison purposes, two additional disks were each coated only withEX704 (Comparison Sample I) and TB3070 (Comparison Sample J),respectively, using this spincoating process. For Comparison Samples Iand J, no perfluoro surfactants were used.

Each of the disks coated with these samples (22, 23, I, and J) was agedin a chamber at 80° C. and 85% relative humidity. Every 500 hours, thedisks were removed and tested for byte error rate by randomly testing 5%of the total memory capacity of each disk. The disks were also testedfor abrasion resistance as well as visually inspected for haze anddelamination prior to aging and after 1500 hours of aging. The resultsfor the byte error rate testing were as follows:

                  TABLE III*                                                      ______________________________________                                        Sample t = 0    t = 500  t = 1000                                                                             t = 1500                                                                             % Change                               ______________________________________                                        22**   1.3      1.2      1.5    2.1     75                                    23     0.9      1.3      1.5    2.3    150                                    I      0.7      1.0      1.9    4.3    500                                    J      0.8      0.0      1.1    1.9    120                                    ______________________________________                                         *values are expressed as the number of errors per 100,000 bytes.              **values for Sample 22 are reported as an average of two trials.         

The results of the abrasion resistance testing and the visual inspectionwere as follows:

                  TABLE IV                                                        ______________________________________                                               t = 0             t = 1500                                             Sample   abrasion   visual   abrasion                                                                              visual                                   ______________________________________                                        22       excellent* good**   excellent                                                                             good                                     23       good       good     good    good                                     I        excellent  good     excellent                                                                             good                                     J        good       good     good    good                                     ______________________________________                                         *"excellent" means no scratches were visually observed.                       **"good" means some scratches, but no haze, were visually observed.      

Other embodiments of this invention will be apparent to those skilled inthe art from a consideration of this specification or from practice ofthe invention disclosed herein. Various omissions, modifications, andchanges to the principles described herein may be made by one skilled inthe art without departing from the true scope and spirit of theinvention which is indicated by the following claims.

What is claimed is:
 1. An optical recording disk having an abrasionresistant, transparent antistatic hard coat layer provided on at leastone surface of the disk, wherein the hard coat layer is a curedcomposition obtained form ingredients comprising(a) 100 parts by weightof nonfluorinated, copolymerizable, radiation curable prepolymers; (b)from 0.5 to 5.0 parts by weight of a nonionic perfluoro surfactant; and(c) from 0.5 to 5.0 parts by weight of an ionic perfluoro surfactant. 2.The optical recording disk of claim 1, wherein the nonionic perfluorosurfactant comprises a perfluoro segment of 4 to 16 carbon atoms.
 3. Theoptical recording disk of claim 2, wherein the perfluoro segment of thenonionic perfluoro surfactant is C₈ F₁₇.
 4. The optical recording diskof claim 1, wherein the nonionic perfluoro surfactant is ##STR3##
 5. Theoptical recording disk of claim 1, wherein the ionic perfluorosurfactant comprises a perfluoro segment of 4 to 16 carbon atoms.
 6. Theoptical recording disk of claim 5, wherein the perfluoro segment of theionic perfluoro surfactant is C₈ F₁₇.
 7. The optical recording disk ofclaim 1, wherein the ionic perfluoro surfactant is C₈ F₁₇ SO₃ ⁻ Li⁺. 8.The optical recording disk of claim 1, wherein the hard coat layercomprises from 2 to 3 parts by weight of the nonionic perfluorosurfactant per 100 parts by weight of the prepolymers.
 9. The opticalrecording disk of claim 1, wherein the hard coat layer comprises from 2to 3 parts by weight of the ionic perfluoro surfactant per 100 parts byweight of the prepolymers.
 10. The optical recording disk of claim 1,wherein the ionic perfluoro surfactant has a perfluoro segment that isthe same as the perfluoro segment of the nonionic perfluoro surfactant.11. The optical recording disk of claim 10, wherein the perfluoro groupof both surfactants is C₈ F₁₇.
 12. The optical recording disk of claim1, wherein the hard coat layer has a thickness of 1 to 5 microns. 13.The optical recording disk of claim 1, wherein the weight ration of thenonionic perfluoro surfactant to the ionic perfluoro surfactant is about1:1.